Retaining wall structures that use horizontally positioned soil inclusions to reinforce the earth mass in combination with a facing element are referred to as Mechanically Stabilized Earth (MSE) structures. MSE can be used for various applications including retaining walls, bridge abutments, dams, seawalls, and dikes.
MSE has evolved from isolated steel strips used as reinforcements to include metallic grid reinforcements and, most recently, geosynthetic reinforcements. The basic MSE technology is a repetitive process where layers of soil, soil reinforcing and facing are placed one a top the other until a desired height of the earthen structure is achieved. MSE technology has evolved to include a method of construction where an earthen structure with a wire facing element is constructed and, after a predetermined time, a concrete panel is attached to the wire faced earthen structure. This type of MSE construction consists of two stages. First, soil reinforcing elements and backfill material are combined to form an earthen structure held into place by a series of welded wire grids, or other suitable structures. In some applications, the wire grids may be coupled to the soil reinforcing elements thereby holding the earthen formation shape. Second, a concrete wall is constructed a short distance from the earthen structural wall. The concrete wall is then attached in several locations to the earthen formation by a variety of means. In one example, a series of turnbuckle systems are coupled to the back side of the concrete wall and also to the soil reinforcing elements. Outward movement of the wall is prevented via this attachment.
MSE walls derive their strength and stability from the frictional and mechanical interaction between the backfill material and the soil reinforcement elements, resulting in a permanent and predictable load transfer from backfill to reinforcements. The reinforcing elements used can include steel and/or geosynthetics. Originally, long steel strips 50 to 120 mm (2 to 5 in) wide were used as reinforcement. These strips were sometimes ribbed, although not always, to provide added resistance. In some applications, steel grids or meshes have also been used as reinforcement elements. Several types of geosynthetics can be used including geogrids and geotextiles.
Typically the concrete wall may be formed in at least two ways. First, the wall may consist of a uniform, unbroken expanse of concrete or the like which is poured on site. Second, the wall may comprise a plurality of manufactured interlocking precast concrete panels or wall modules which are assembled into interlocking relationship once on site. The several precast concrete panels are stacked end on end on site, thus forming a concrete wall.
In a typical MSE system, the securing means between the concrete wall and the earthen formation is normally attached to the soil reinforcing elements housed in the backfill. This limits the number, length and rotation of the several connectors. In addition, it limits any necessary means of fixing subsequent problems that may arise during the installation of the concrete panels or settlement of any portion of the wall system.